This composite of enhanced color images of Pluto (lower right) and Charon (upper left), taken by NASA's New Horizons spacecraft on July 14, 2015, highlights the wide range of surface features on the small worlds. Working with the New Horizons mission team, the International Astronomical Union (IAU) has approved the themes to be used for naming the surface features on Pluto and its moons. (Credit: NASA/JHUAPL/SwRI)

Kirby Runyon cuts the figure of an astronaut, and you just know that he would be helpful in a bar fight, but you also get the impression that he would defuse things for you before it got that far. He is a young man and a newly-minted Ph.D., and with an abstract submitted to the Lunar and Planetary Science Conference late last March, stepped into a white-hot spotlight with an international audience. He and one of his co-authors, Alan Stern, the principal investigator on the New Horizons mission to Pluto, have taken a swing at the question of planethood.

Runyon’s definition of a planet is a single sentence in length: “A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has enough gravitation to be round due to hydrostatic equilibrium regardless of its orbital parameters.” In other words, a planet is a ball in space that’s not a star. That means, yes, Pluto is a planet. It also means that the Moon is a planet. Europa is a planet. Ganymede is a planet.

In comparison, the newly-established definition of a planet by the International Astronomical Union states: “A planet is a celestial body that is in orbit around the Sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and has cleared the neighborhood around its orbit.” In this regime, were Ganymede knocked from orbit around Jupiter and into orbit around the Sun, it would still be Ganymede, but might suddenly, according to the IAU, be a planet. At an instinctive level, this feels wrong, like saying that if a dog climbed onto a bookshelf, it would then be a cat. The astronomy view categorizes a planet based on what it orbits. Runyon’s assertion is that a planet should be defined by what it is.

What imbues Runyon’s definition with resilience is that it doesn’t seek to somehow overturn that of the IAU, and he has no intention of submitting it to the IAU for consideration. “If certain types of astronomers want to have an orbital dynamic definition of a planet,” he says, “and that’s useful to them, fine. But most scientist who study planets are more aligned now with the geosciences than they are with astronomical scientists. And that definition of ‘planet’ just isn’t useful to us. It doesn’t help us communicate our ideas.” Informally, planetary scientists have always called all sorts of bodies in space “planets.” But formally, too, in peer-reviewed literature, technical moons are called planets. Runyon lists scores of such references made both before and after the IAU redefinition.

This is in part about the coming of age of planetary science. It is a young field, a single generation old, the plucky upstart once the exclusive domain of physics, then of astronomy, but whose constituent sciences now include geology, chemistry, and biology. Mars was once something you look up at, a dot in the sky. Celestial. Now it’s something you look down on from orbit, or across from the surface. It’s terrestrial. Geophysical.

“Carl Sagan said, ‘In science there are no authorities; at most, there are experts,’” Runyon tells me as we talk outside the convention center where he presented abstract. This isn’t a heated argument, and he counts Mike Brown, the famed “Pluto Killer,” as a friendly correspondent. Let the astronomers do what they want, he explains brightly, but leave us—i.e., geologists—out of it. The concept isn’t even unique. “To astronomers studying the composition of stars and nebulae, especially stars, they call anything heavier than element number two―anything heavier than helium―a metal. That’s just a convenient word for them. No one’s fighting about this,” says Runyon. “They know what they mean when they say metal, and it’s different from the common definition. You take the spectra of stars, and you see there’s oxygen and nitrogen and argon in stars’ atmospheres, you call that a high metallicity star. And that’s fine. Metallurgists aren’t fighting them over the word metal.”

This matters beyond the arcane world of scientific abstracts and poster sessions. Very rarely does a scientific debate spill into the public sphere and draw not only keen interest, but steely opinions. Evolution, certainly. The age of the Earth in some religious circles. But you don’t often see finger-pointed assertions over scientific nomenclature. The Washington Post doesn’t give a thousand words to disagreements over the precise definition of “suevites” (a type of rock formed during impact events) though scientists do debate its usage. This matter of Pluto, however, is both consequential and easily understood. Everyone has their own take on whether it is a planet.

Under Runyon’s definition, there are at least 110 planets in the solar system. This seems at once absurd, but resolves into something very interesting. He explains that the idea of planets being something you must memorize is a pointless exercise. Memorizing the periodic table of elements doesn’t make one a chemist. But just as the table itself is elegant and informative, plot all the planets on a table and you get something equally elegant. Terrestrial planets, gas giant planets, ice giant planets, dwarf planets, exoplanets, each arranged and subgrouped with common characteristics. Europa so plotted might be categorized as an icy dwarf satellite planet.

And suddenly, rather than rote memorization, Mercury, Venus, Earth, and so on, you have an ambitious and quite possibly tectonic effect on education. Rather than eliminating things to learn―Pluto itself has been rendered ontologically unsound since the IAU announcement, disappearing not only from textbooks but also consumer goods and media―you have the introduction of worlds that rarely appear in the classroom, Makemake, Mimas, Miranda and more. The conversation about Pluto has arguably been a net positive for the public, whose idea of the solar system is too often limited to plastic beads on wires circling a light bulb.

An invested public with a robust science education is as important as ever before. Even with our pedestrian terrestrial political problems, it’s a good time to be a human being. We stand on a precipice of sorts, in which asteroids, planets―even stars―are accessible not only by scientists with instrument-laden spacecraft, but soon by the working man and woman. One easily imagines a real future in the lifetimes of our children in which “planet” relates not to hydrostatic equilibria or accretion disc formation, but by something inherently more utilitarian. Planet will be a shorthand for something vaguely accessible by humans and our tools for long durations. Somewhere useful. Somewhere with a horizon commensurate to that which the human mind has evolved to expect. Can I drive a shovel into the body and pull up raw materials? In plain science fiction terms, can I land my spaceship on it? Is it round and can I fly my gas mining barge through it?

In both the very short term and very long, what is or isn’t a planet is not particularly important. In the middle, however, in our present-day future in which dot-com billionaires want to put people in space, and not in capsules of three, but transports of hundreds, and they say this with authority and are investing the capital to make it a reality, suddenly “planet” is a word due to be handed back to the people. Given a better spacesuit, if I lived on Titan or Mars, is there a measurable difference in bodies? This land is your land.

Though you might not recognize her name, you know Margaret Hamilton’s work, and you quite possibly know her face. She led the team responsible for the on-board flight software for the Apollo command module and lunar module. A black-and-white photograph of Hamilton standing next to a stack of code has reached iconic status, for reasons obvious: here is a woman pioneering the field of computer science at a time when the discipline was almost exclusively male; a laboratory director of software engineering before “software engineer” even existed as a job title; and an achievement to her name that defies comparison with any other human endeavor.

She didn’t stop at landing astronauts on the moon. She contributed also to Skylab, the first American space station, and to the space shuttle. In 1986, she founded Hamilton Technologies, Inc., a software development firm. Last year, she was awarded the Presidential Medal of Freedom for her work on the Apollo program and for her contributions in the field of computer science to “asynchronous software, priority scheduling and priority displays, and human-in-the-loop decision capability, which set the foundation for modern, ultra-reliable software design and engineering.”

A new picture book about Hamilton was published last month by Knopf Books for Young Readers. Written by Dean Robbins and illustrated by Lucy Knisley, Margaret and the Moon recounts Hamilton’s story and brings children to the harrowing landing of the Eagle. Computer science doesn’t come immediately to mind as a rich field from which children’s literature might grow, and yet Robbins and Knisley deftly tell a story that is at once moving and exciting. It is a testament to the skill of the author and illustrator that the book will be for many readers the first biography they ever read, an early introduction to the Apollo program, and an inspiring story of how science and engineering are done — and the book excels at all three.

In an interview by email, Hamilton tells me about her journey to the Apollo program, equality in STEM, and her contributions to the computer science discipline. It has been edited lightly for length and clarity.

Margaret Hamilton with her code (Credit: MIT Museum)

What were the circumstances of the famous photo of you standing next to that towering stack of code?

MHH: The photo was part of the information that MIT provided to the news media during the time of the Apollo 11 mission. The following was excerpted from a description of the photo in an MIT document: “Taken by the MIT Instrumentation Lab photographer in 1969…Margaret is shown standing beside listings of the software developed by her and the team she was in charge of, the Lunar Module (LM) and Command Module (CM) on-board flight software team”.

Each listing in the stack of listings contained Apollo guidance computer source code. For every mission there were two listings; one for the command module and one for the lunar module. Two of the listings were for Apollo 11, one for the Apollo 11 command module and one for the Apollo 11 lunar module. Other listings in the stack contained source code for future “to be” missions (e.g., Apollo 12, Apollo 13…) that we had been working on concurrently along with the source code for Apollo 11.

Is the Apollo program something that pursued you, or did you pursue it? In other words, how does one join the most ambitious engineering endeavor in human history?

MHH: At the time, I was working at MIT’s Lincoln Labs on the Semi-Automatic Ground Environment air defense system, developing radar registration surveillance software for detecting potential enemy planes, on the first AN/FSQ-7 computer (the XD-1). I had always planned to attend graduate school at Brandeis and major in abstract math, but I got sidetracked. Sometime within the 1963–1964 timeframe, I heard the news that MIT had received a contract from NASA to develop the software for “sending man” to the moon, and that MIT was looking for people to work on this project. I immediately called MIT to see if I could be involved in what sounded like the opportunity of a lifetime. Within hours, I set up interviews with two project managers at MIT. Both of them offered me a position on the same day as the interviews. I did not want to hurt anyone’s feelings, so I told them to flip a coin to decide which group would hire me — hoping for the project manager to win the coin toss, who, in the end, did win. Fortunately, that is what happened, and I was on my way.

There is a greater effort today to correct the gender imbalance in the fields of STEM. What advice would you give to aspiring scientists and engineers?

MHH: The type of experience and education one has before entering the fields of STEM as well as other fields is key. I have found it helps to have both a “streetwise” experience and a formal education. From a streetwise perspective, the more jobs a young person has (and the more varied), the better prepared one is for going out into the world. Learning how to work with and getting used to being around different kinds of personalities and challenges helps one to have the flexibility needed to understand others, and to deal with the unexpected. It provides a better foundation from which to make career choices, including who you choose to work with and for whom you choose to work.

Regarding the formal part of education, one would of course want to take courses directly related to the particular field of STEM of interest (e.g., computer science). But, it is also important to learn and be around other kinds of things like music, art, philosophy, history and formal linguistics; any of which could help improve one’s being an excellent problem solver; and to have a more global perspective on things. The ultimate goal is learning how to think.

Women cannot be expected to solve the gender imbalance problem alone — especially on an individual-by-individual basis. Too often it is the symptoms of the problem that are being addressed by well-meaning efforts today, when the real problem has been and still is our culture. Things are still being done (and accepted as such) out of ignorance. It is not uncommon for an organization to pay women lower salaries than men for the same position, and to relegate women to the lower positions in an organization. And if not, women often have to work or fight harder than their male counterparts to be an exception. Most would agree that the STEM fields are still dominated by men; that discrimination does exist. In fact, some things seem to have gone backwards and are more difficult now than they were in the sixties. Some ways in which discrimination manifests itself can be quite different today — especially now that we have the internet.

Unfortunately, various types of communication over the internet can serve as convenient places to “hide” in, encouraging “faceless,” pervasive practices, making it harder than in earlier days to confront those intent on perpetuating disinformation that can be quite harmful to those on the receiving end. A case in point is the use of historical revisionism, in any form conceivable, to minimize the accomplishments of an individual or a group of individuals; a not uncommon practice when it comes to the affect it has on women and minorities. Solving just this one part of the problem, itself, is indeed a challenge that can only be totally addressed at large.

One seemingly small event can change everything, for better or worse, because everything is somehow related to everything else. When the most powerful and influential leaders and organizations in the world make it possible for women to hold the highest positions (not “almost” the highest) in their organizations equal (not “almost” equal) to what is available to men, we all benefit, including the leaders and organizations themselves. When large corporations refuse to conduct business with and within countries who do not allow women to have the same rights as men, we all benefit. The more all of us work to uncover discriminatory practices and the more those in power promote non-discriminatory practices as being a positive thing, the more we all benefit.

Margaret Hamilton in an Apollo command module (Credit: NASA)

What most worried you during development of the Apollo software, and how did you and your team solve it?

MHH: The greatest challenge was that our software had to be man-rated; which meant lives were at stake. Failure was not an option. Not only did it have to work; it had to work the first time. Not only did the software, itself, have to be ultra-reliable, but the software would need to be able to detect an error and recover from it in real time. It did not disappoint.

The task at hand included developing and integrating all of the software for the command module, the lunar module and the systems software shared between, and residing within, both the command and lunar module; making sure that everything would play together and that there were no integration, communication, or interface conflicts (i.e., data, timing or priority conflicts). Updates, submitted from hundreds of people, were continuously being made over time and over the many releases for every mission; making sure that the software would successfully interface to, and work together with, all the other systems including the hardware, peopleware and missionware.

Because of the never-ending focus on making everything as perfect as possible, anything to do with the prevention of errors was not only not off the table, but it was top priority both during development and during real-time where it was necessary to have the flexibility to be able to detect anything unexpected and recover from it at any time in a real mission. To meet the challenge, the software was developed with an ongoing, overarching focus on finding ways to capitalize on the asynchronous and distributed functionality of the system at large in order to perfect the more systems-oriented aspects of the flight software. Such was the case with the flight software’s system-wide snapshot rollback capabilities and priority displays together with its man-in-the-loop techniques. Our software was designed to be asynchronous in order to have the flexibility to handle the unpredictable, and in order that higher priority jobs would have the capability to interrupt lower priority jobs, based on events as they happened (especially in the case of an emergency).

Each mission was exciting in its own right, but Apollo 11 was special; we had never landed on the moon before. Just as the astronauts were about to land on the moon, everything was going according to plan until something totally unexpected happened. All of a sudden, the on-board flight computer became overtaxed. The software’s priority displays of 1201 and 1202 alarms interrupted the astronaut’s normal mission displays to warn them that there was an emergency, allowing NASA’s Mission Control to understand what was happening, and alerting the astronauts to place the rendezvous radar switch in the right position. The priority displays gave the astronauts a go/no go decision (to land or not to land).

It quickly became clear that the software was not only informing everyone that there was a hardware-related problem, but that the software was compensating for it. With only minutes to spare, the decision was made to go for the landing. The rest is history. The Apollo 11’s crew became the first humans to walk on the moon, and our software became the first software to land on the moon. An explanation of what happened, and the steps taken by the on-board flight software to “continue on” to landing are briefly described in my letter to the editor, “Computer Got Loaded”, published in the March 1, 1971 issue of Datamation.

The development and deployment of this functionality would not have been possible without an integrated system of systems (and teams) approach to systems reliability and the innovative contributions made by the other groups to support our systems-software team in making this become a reality. The hardware team at MIT changed their hardware and the mission planning team in Houston changed their astronaut procedures, both working closely with us to accommodate the priority displays for both the command and lunar modules for any kind of emergency and throughout any mission. In addition, the people at Mission Control were well prepared to know what to do should the astronauts be interrupted with the priority displays.

Since it was not possible (certainly not practical) on Apollo for us to test the software “before the fact” by flying an actual mission, it was necessary for us to test our software by developing a mix of hardware and digital simulations of every (and all aspects of an) Apollo mission which included man-in-the-loop simulations (with real or simulated human interaction); and variations of real or simulated hardware and their integration.

Astronauts who have walked on the moon often describe a certain listlessness once they get home. As an engineer key to that achievement, are you left with a similar feeling? What sort of feeling follows?

MHH: Of course, I would be hard put to even begin to compare feelings of my own to that of an astronaut who walked on the moon! Do you mean by a certain listlessness that I may have experienced a letdown or feeling of depression, because of the fact that nothing could ever follow that could be as exciting? I do not remember a time, following a major event (like landing on the moon) or a major project (like Apollo), when there was a real chance (or when I took a chance) to reminisce and miss the action. There was always something happening immediately thereafter that seemed to be exciting in its own right.

I have always been more “wrapped up” than not, with wasting little time in capturing lessons learned from an experience and doing something about it so that we could apply that knowledge on the adventures to follow. Towards this end, I have found that it helps to focus on learning from the past, not living in it. There was always an adventure to follow that would have its own kind of excitement. I do want to say, however, that what we have been doing over the years with our computer science-related work is much more exciting because of the lessons we learned from Apollo.

Describe your work on Skylab and the space shuttle.

MHH: Skylab was a continuation of the Apollo command module on-board flight software, with new software added for new Skylab requirements. We defined systems software requirements for the Skylab and the Space Shuttle on-board flight software as a result of many of the lessons we had learned from Apollo. Among other things, we performed an empirical study of the Apollo on-board flight software development effort, resulting in formalizing lessons learned. Part of the requirements for Skylab and the Space Shuttle originated from this work.

As a pioneer in the field, what would you say is your greatest contribution to the discipline of computer science?

MHH: For whatever success I have experienced in my work, the credit goes not only to those I have learned so much from and have worked with, but also to the errors I have had the opportunity of having had some responsibility in making, without which we would not have been able to learn the things we did — some with great drama and fanfare, and often with a large enough audience to not want such a thing to ever to happen again!

Having been through some amazing experiences such as those involved with the Apollo on-board flight software, one could not help but do something about learning from them. With initial funding from NASA and the Department of Defense (including the Air Force, the Navy, and the Army), we performed an empirical study of the Apollo effort. This resulted in a systems theory, based upon a concept of control, that has continued to evolve based on lessons learned from Apollo and later projects. From its axioms, we derived a universal systems language together with its automation and its preventative development paradigm.

We continue to discover new properties in systems defined with this language. Among other things, we learned that with the use of the language there are no interface errors in a system definition and its derivatives (one of which is its software); and integration within a definition, and from systems to software, is inherent. Along the way, it became clear one day that the root problem with traditional approaches is that they support users in “fixing up wrong things” rather than in “doing things in the right way in the first place.” With a preventative paradigm, instead of looking for more ways to test for errors, and continuing to test for errors late into the life cycle, the majority of errors including all interface errors are not allowed into a system in the first place, just by the way it is defined. Testing for non-existent errors becomes an obsolete endeavor. For each new property discovered, that, in essence, “comes along for the ride,” there is the realization of something (e.g., testing for interface errors) that will no longer be necessary as part of the system’s own development process.

Over at The Atlantic, I write about the looming, phenomenally stupid pivot by NASA away from Mars and toward the moon. A snippet:

American moon partisans owe a debt to Europe, which has tended the lunar flame during the ascent of Mars. Perhaps the most prominent moon advocate on Earth is Jan Woerner, the director general of the European Space Agency. Since assuming the post, he has argued persuasively that a “lunar village” is the natural successor to the aging International Space Station. It would be, in his view, a celestial point of harmony for a terrestrial species in discord. There is a problem, however: the Europeans have committed virtually no money to a moon village, and Russia, ESA's would-be partner in the venture, has no money to commit. They have already been forced to downsize their presence on the ISS due to costs, and have delayed plans for robotic exploration of the moon. (The head of the Russian space agency admits that Russia “does not have financial capabilities for advanced space projects.”) Lacking unity among member states, to say nothing of technology development and financial resources, what ESA really needs is for the United States to fund and spearhead such an effort. NASA's sights, however, are firmly fixed on Mars. With the presidential transition, however, and a new NASA director still to be appointed, lunar champions at home and abroad see an opportunity to abandon the Journey to Mars program and set sights a little closer to the Earth.

To that end, ESA is on a moon base public-relations offensive, from the light and easy (magazine spreads and aspirational illustrations) to bare-knuckled politics (publicly pressing the NASA administrator on the issue.) The overt message from Paris, where ESA is headquartered, is: We're doing this. The subtext is: While NASA plans a fantasy mission to Mars that will never happen, the rest of the world will be driving moon buggies and mining helium-3. But ESA’s campaign is powered by handwavium, and for all the illustrations of lunar domes and our great big blue marble over the horizon, progress on the moon base ends at Photoshop. If the U.S. doesn’t build the base, it won’t get built.

Earlier this year, I covered the rocket launch of OSIRIS-REx, a spacecraft that will visit an asteroid, study it, collect a sample, and return to Earth. My account of the launch has been published by The Week. I really do think it's the best thing I've ever written and I hope you enjoy. Here is a little snippet:

The tail of flame is about as long as the rocket itself, but it is not orange. It's not even fire, really, as you understand fire to be. It is white. It hurts the eyes. It's like staring at a concentrated burst of manufactured sun. It's not the flamethrower's discharge, but that of the welding torch. It is blinding. It doesn't billow. It's all business, this white welding torch. So pure and focused and controlled.

The smoke is produced by ignited liquid oxygen and liquid kerosene. It is the color of cigarette smoke, and at ignition it shrouds the launch complex bottom to top, pad to candlestick-like lightning rods. The rocket rises above. The smoke follows the rocket up. It's a skywriter, this thing, drawing smoothly some great, fine arc to heaven. The higher it gets, the whiter the smoke, purer, purer, purer, until at last it seems humankind has surpassed the cloud itself as an object of stainless wonder against a curtain of blue.

While covering the 47th Lunar and Planetary Science Conference in The Woodlands, Texas last month, I wrote several pieces on various happenings and findings in and about our solar system. Here are a few snippets of pieces that resulted, published by mental_floss. (And let me just add that if you've never had to explain nuclear spectroscopy for a general readership, you just haven't lived yet.)
Every Inch of Ceres Is Now Mapped—and Yet Mysteries Remain

Dawn is loaded with delicate instruments to help decipher the dwarf planet's secrets. The Gamma Ray and Neutron Detector (GRaND) maps elements on the asteroid so that scientists can make sense of the surface and processes at work. The instrument works like this. Galactic cosmic rays smack into the regolith (the loose surface layer; on Earth, think: dirt), and interactions with the surface lead to emissions of neutrons and gamma rays. GRaND detects these emissions as they bounce into space. Neutrons at different energy levels correspond to different surface elements.

During the regolith interaction, when the cosmic rays hit the nucleus of an atom, the nucleus explodes, sending neutrons and protons in all directions. Some neutrons escape the regolith, some smash into other nuclei. Here's where it gets interesting. If a neutron hits the nucleus of a hydrogen atom, it loses energy in the interaction, similar to the way a cue ball stops when it hits another ball in a game of pool. When GRaND is counting neutrons, therefore, lower numbers suggest more hydrogen.

That's what is shown on the above map [not pictured in this blog snippet—dwb], which is color-coded for the presence of hydrogen. (Blue is more; red is less.) The area in blue is the north pole of Ceres, and as the map reveals, it's teeming with hydrogen, relatively speaking. This indicates the presence of water ice—H2O—near the dwarf planet’s surface. This is the first time such ice has been detected, and the finding is consistent with longstanding scientific predictions. Planetary scientists will continue analyzing the data collected by GRaND and other instruments in order to better understand the origin and evolution of Ceres.

You have to admire the effort it took to build the acronym VERITAS, which is short for Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy. VERITAS is a proposed mission to visit Venus and figure out where things went so wrong. Above the clouds, Venus is far more hospitable to humans than Mars. Its temperature and weather aren't all that different from Earth, and scientists have proposed colonizing Venus with a series of airships. Below the clouds, however, Venus is a living hell. With surface temperatures near 900°F, it's hotter than Mercury, and its south pole is consumed by a rapacious, undying superstorm. The questions VERITAS intends to answer involve the state of Venus's geologic activity; its tectonic characteristics in comparison to Earth; and the evidence of past water at its surface.

[Blog note: My favorite line in the piece was cut, and I'll share it here: "Venus is the place where people in hell are afraid they'll go when the die."]

Think back to the volcano diorama you made in grade school. Little mountain, maybe trees and plastic dinosaurs (because every grade school project is improved with dinosaurs). In our model, red food coloring, baking soda, and vinegar are meant to simulate what's going on when a volcano erupts. Magma, which is molten rock and volatiles, builds up pressure until the ground gives way and it spews forth from vents in the Earth's surface.

This sometimes looks like the occasional, seemingly apocalyptic eruptions of Volcán de Colima in Mexico. Sometimes it looks like the gentle flows in the Pacific islands where you can hire a tour guide and observe lava streams as they roll along.

A cryovolcano isn't all that different. Like an Earth volcano, it results from pressure beneath a celestial surface. Rather than molten rock, however cryovolcanoes are the eruptions of moltenice, sometimes called cryomagma. Ice volcanoes can erupt violently or flow gently, just like the volcanoes on Earth. The gentle "tour guide" eruptions are believed to be like flowing slurries.

[Blog note: Bring tequila, triple sec, salt, and a bag of limes and you can throw the best rita party on Pluto.]

“Pluto is a very complicated place,” said Richard Binzel, a professor at MIT and a co-investigator of the New Horizons mission. “We’ve been trying to go back to basics to see how seasons and climate might be shaping Pluto.”

Scientists have worked out the location and nature of Pluto’s tropics—a concept that might seem unlikely on a frozen planet 6 billion kilometers from the Sun. To understand what “tropics” means in this context, consider the axial tilt of the Earth, which is 23.5 degrees. The tilt is the reason that our planet experiences seasons, and over the course of a year, the Sun is directly over one of any latitude between the Tropic of Cancer (23.5 degrees north) and the Tropic of Capricorn (23.5 degrees south). That’s why the tropics are known for their warm weather.

For comparison, Pluto’s axial tilt is 120 degrees. This makes the range of tropical latitudes much broader than Earth's... Moreover, just as the axial tilt of the Earth gives us arctic circles with their attending stretches of dark winter or midnight Sun, Pluto's extreme tilt creates arctic circles as well—circles that reach nearly to its equator. “If Earth were tilted by same amount as Pluto, we [in Texas] would be in the arctic zone on Earth," Binzel said. A result of the overlapping arctic and tropical zones is that Pluto actually has "tropical arctic" bands.

Here is an actual problem that scientists have tackled, not as consultants for some sure-fire science fiction blockbuster, but rather, in order to put together a very real NASA mission: How do we launch a submarine into space, send it to another world, and drop it into an extraterrestrial lake?

As it turns out, a lot of work on the problem has already been done. The traditional shape of a submarine doesn't lend itself to the classic entry shell seen previously with the Mars landers. The Titan submarine team soon realized, however, that the submarine would fit quite nicely inside the cargo bay of a scaled-down space shuttle. Better still, DARPA—the Defense Advanced Research Projects Agency—has already built a scaled-down space shuttle, and it's flying today. It is called the X-37B—and the submarine would fit inside it.

The entry velocities for a mission to Titan would be the same as Earth orbital velocities, something the X-37B and its thermal protection can already handle. ("For [this phase of] the study, we just said, 'Sure, we could make that work,'" Lorenz explained at the forum.) Such an entry vehicle would be especially useful in that it could fly to a designated spot without dealing with the winds and consequent uncertainties that a typical parachute descent entry would have to overcome.

Next, the Titan team considered extracting the submarine from the back of the vehicle, much in the same way the U.S. Air Force pushes a MOAB from a C-130. They also looked at ditching tests conducted by NASA in the event that the space shuttle would ever have to land on water. A splashdown on Titan of their spacecraft, they found, would be quite forgiving, and if they attempted such a landing, they could simply flood the entry vehicle, let it sink, open the back, and let the submarine swim out into the sea. From there, the vehicle would conduct preliminary sea trials to discern maneuverability, and then get underway.

[Blog note: Ralph Lorenz, the project scientist on the mission study, had a magnificent quote that's elsewhere in the piece, but that I wanted to share here: "The virtue of this study is that you just need to say those words—Titan submarine—and everyone kind of gets that it's out there, it's interesting, and there's a lot of exciting potential."]

This is my second year covering the Lunar and Planetary Science Conference, an annual gathering in Houston, Texas of the world's planetary scientists. Most of my coverage will appear at mental_floss, and I'll post links as they go live. I suspect if you've arrived here, it's from one of my m_f pieces. If you enjoyed that work, here are a few pieces of note that I've written about planetary science and external issues affecting the field.
The Scientists Who Conquered Pluto, The Week

We know well the way astronauts think because we've studied them for so long — lionized them, rightfully, in books and movies and on television. We understand the human adventure. We understand that astronauts train hard and while in space live in pretty miserable conditions. But we also understand the glory of being an astronaut. They are humanity's ambassadors. They are exploring the final frontier. They've played golf on themoon! But what of these people — the New Horizons people, these spacecraft pilots and planetary scientists who study the outer reaches of the solar system? What can be made of them? Alice Bowman said the words, "We are outbound from Pluto." Has a more breathtaking string of words ever been uttered?

The lighting of Pluto is a coming of age for humankind. It is the end of one thing — proving that we can visit any world we so choose — and the beginning of something profound: looking outward, beyond the orbits of the planets, with an eye toward active exploration. Contrary to common lamentations, NASA is not an agency flush with cash (its total budget takes up less than one half of one percent of the federal budget), and it is not an agency adrift. We are, in fact, living in a golden age of space exploration. In a five-year span, humanity will have visited the farthest planet in the solar system and set a course for the Kuiper Belt (long hypothesized, but only discovered in 1992); executed a hair-raising entry, descent, and landing of the Mars Science Laboratory; and rewritten the books on Mercury and Saturn, based on the astonishing discoveries of MESSENGER and Cassini, respectively.

Two years ago, NASA’s Mars Atmosphere and Volatile Evolution (Maven) spacecraft, a $671 million mission to study the composition of the Martian upper atmosphere, sat at Kennedy Space Center ready to go to space, but with no one there to push the button. Congress and the Obama administration were competing to see who would blink first, but the planets weren’t waiting. If Maven didn’t lift off before the close of its launch window, the position of Mars relative to Earth would force a launch delay of 26 months. This would have had repercussions for Mars missions subsequent to Maven, as well as for scientists awaiting data for study and analysis.

Michoud looks like a place where things are built. Spacecraft, yes, and rockets—the biggest ever imagined—but things all the same. With only slight changes, it could be a place where cars are manufactured, or supercomputers, or valves, or motors. Michoud is like the world's greatest high school metal shop, only instead of turning wrenches to automatic transmissions, the men and women here apply tools to spacecraft. Sheets of metal roll in the front door, and spaceships and rockets roll out the back.

The facility is located on the outskirts of New Orleans, amidst vast footprints of vacant land. Across the street from Michoud is a Folgers Coffee plant, leaving the air outside redolent with the soft bitterness of a newly opened bag of ground coffee. That itself is striking—the mix of coffee, concrete, cars, and cranes. This is where science fiction is realized, and it's all so normal. The workers here are some of the smartest people in the world doing some of the most challenging and important work in the world, but they seem like true workers in the grandest human sense of the word, the kinds of men and women otherwise seen with sleeves rolled up on wartime propaganda posters. Together we can do it! Keep 'em firing!

Mark Kirasich, the program manager of Orion, described the Orion team as the "craftsmen of the 21st century." In some beautiful future of humanity, this is the job where blue collar men and women punch in at 9, ply their trade, punch out, and grab beers before flying home on jetpacks. Today they build Orion spacecraft and the Space Launch System rockets that will take them into space. Previously, they built the 15-story external fuel tanks for the space shuttle, and the first stage of the Saturn V rockets that sent men to the Moon.

Last week I visited NASA Michoud Assembly Facility in New Orleans to view the newly-built Orion pressure vessel. I found the whole thing to be a deeply moving experience, and a glimpse of the kind of future we all want desperately for our grandchildren, and for the human species. I am very proud of this essay that came out of the event. It's published at Mental Floss, and I hope it finds a good audience.
A little sample:

Michoud looks like a place where things are built. Spacecraft, yes, and rockets—the biggest ever imagined—but things all the same. With only slight changes, it could be a place where cars are manufactured, or supercomputers, or valves, or motors. Michoud is like the world's greatest high school metal shop, only instead of turning wrenches to automatic transmissions, the men and women here apply tools to spacecraft. Sheets of metal roll in the front door, and spaceships and rockets roll out the back.

The facility is located on the outskirts of New Orleans, amidst vast footprints of vacant land. Across the street from Michoud is a Folgers Coffee plant, leaving the air outside redolent with the soft bitterness of a newly opened bag of ground coffee. That itself is striking—the mix of coffee, concrete, cars, and cranes. This is where science fiction is realized, and it's all so normal. The workers here are some of the smartest people in the world doing some of the most challenging and important work in the world, but they seem like true workers in the grandest human sense of the word, the kinds of men and women otherwise seen with sleeves rolled up on wartime propaganda posters. Together we can do it! Keep 'em firing!

Today's edition of the New York Times contains my very first op-ed for them, on how budgetary uncertainties harm the American space program.

The United States asks NASA to do an extraordinary amount with very little money. Explore Mars, document climate change, stop doomsday asteroids, find life on Europa — all for less than one-half of 1 percent of the federal budget. But budget uncertainties on Capitol Hill, including delays in federal appropriations legislation and temporary government shutdowns, measurably harm the American space program. Even the threat of a shutdown can have a far-reaching impact on scientific projects, often in unexpected ways.

Last month I attended a NASA test of an RS-25 rocket engine. Even weeks later, I think about the event in awe and wonder. The A-1 test stand to which the engine was mounted is impossibly large. The B-2 test stand, which will eventually test an array of four RS-25s, is larger even still. The engine test itself was like experiencing what I can only describe as a peaceful apocalypse. The sound and reverberations and billowing clouds had the all the terrible power and spectacle of what I imagine the end of the world to be like, but there, at NASA Stennis Space Center, the force was put toward the cause of peace and the betterment of humankind. I'm not given to mawkishness about such things, but all I could think the whole time was: If we can do this, we can do anything.
The only other time I've ever felt that way was visiting the Great Wall of China—another impossible human achievement of breathtaking size, scope, and engineering genius. I feel fortunate to have seen two such wonders in a single lifetime.

I wrote a little about the test for Mental Floss:

It was magnificent. The engine was like an inverted volcano. White clouds billowed forth at 13 times the speed of sound, blasting so forcefully that even its component water vapor seemed confused and alarmed. The sound was like a sustained, rolling thunder that you could feel in your teeth, and its timbre dominated even your pulse. The experience was truly awesome in force and effect. The power and fury of the test was terrifying—and yet the RS-25 is perhaps the most peaceful product of the space age thus far. It's not a weapon of war. It powers no ballistic missiles, nuclear or otherwise. It exists only for exploration and the betterment of humankind.

I've embedded a video below. It doesn't come close to capturing the thing. The clouds you see billowing from the engine test stand are made of water vapor. The RS-25 burns liquid oxygen and liquid hydrogen; the engine leaves behind an Earth as clean as it found it.

This week I've been at the Applied Physics Laboratory at Johns Hopkins University, where I am covering the New Horizons flyby of Pluto. It's been humbling and inspiring to witness a landmark achievement in human history: the complete exploration of the classical solar system.

It says so much about the nature of space exploration that one reflexively uses the pronouns "we" and "us" when discussing it. I can think of no other peaceful human endeavor where that is the case.

We didn't map the human genome; scientists did. We did not discover the Higgs boson. Physicists get the credit. When Olympic world records are set, nobody watching from his or her couch says, "Well, it looks like we are faster now." But we went to the moon and we're looking for life on Mars. (Conversely, we invaded Afghanistan. We defeated the Nazis. We fought wars in Iraq and Vietnam. Perhaps the wonder of space exploration is the alter ego to the horror of war.)

In 2011, New Horizons discovered a second moon orbiting Pluto (Kerberos), and a year later a third (Styx). That’s been both exciting and worrying. These moons lack the mass and gravity to keep debris caused by planetary collisions from flying into space, where they could potentially smash into the spacecraft. Debris doesn’t have to be big to be a threat: a piece the size of a grain of rice could prove catastrophic to the probe. Think of a rock hitting your windshield. Now imagine if you were driving 31,000 miles per hour.

The Long Range Reconnaissance Imager, or LORRI, "is essentially a digital camera with a large telephoto telescope—only fortified to operate in the cold, hostile environs near Pluto,” according to the New Horizons team. LORRI is so powerful that on closest approach, it was able to resolve features as small as football fields. The instrument began snapping shots of the Pluto system at the start of 2015 and is responsible for pretty much every shot we’ve seen so far. The camera only takes black-and-white photographs; color filters were left out of the design in order to keep things simple, and to ensure an extremely high light-sensitivity level. (Light levels are 1000 times lower in the Pluto system than on Earth.) The Ralph instrument provides the color data for LORRI images.

We know well the way astronauts think because we've studied them for so long — lionized them, rightfully, in books and movies and on television. We understand the human adventure. We understand that astronauts train hard and while in space live in pretty miserable conditions. But we also understand the glory of being an astronaut. They are humanity's ambassadors. They are exploring the final frontier. They've played golf on the moon! But what of these people — the New Horizons people, these spacecraft pilots and planetary scientists who study the outer reaches of the solar system? What can be made of them? Alice Bowman said the words, "We are outbound from Pluto." Has a more breathtaking string of words ever been uttered?